1. Field of the Invention
The present invention relates to an imaging device, an imaging method, and an image processing device. In particular, the present invention relates to an imaging device, an imaging method, and an image processing device capable of performing restoration processing based on a point spread function.
2. Description of the Related Art
On an image of a subject photographed through an optical imaging system, sometimes, a so-called point spread phenomenon may be observed. The point spread phenomenon is a phenomenon that a point subject is slightly enlarged by an effect such as aberration or diffraction caused by the optical imaging system. A function, which indicates a response to a point light source of the optical system, is referred to as a point spread function (PSF). This function is known as a parameter having an influence on resolution degradation (blurring) of a photographed image.
A photographed image, of which image quality is lowered due to the point spread phenomenon, is subjected to restoration processing (point image restoration processing) based on the PSF, and thereby image quality of the image can be restored. The point image restoration processing is processing of acquiring degradation characteristics (point image characteristics), which are caused by aberration and the like of the lens (optical system), in advance and canceling out the point spread of the photographed image through image processing using a restoration filter corresponding to the point image characteristics.
There have been proposed various techniques of the point image restoration processing. For example, JP2010-087862A discloses an image processing device capable of appropriately restoring a subject image even when a subject distance is unclear. The image processing device performs correction processing on an image in accordance with a degree of opening of an aperture stop of an aperture stop section provided in the optical system, by using dependency of the optical transfer function of the optical system on the degree of opening of the aperture stop.
JP2012-065114A discloses an imaging device capable of extending a depth of field without causing artifacts by minimizing processing time periods for positioning, synthesis, and the like. The imaging device calculates the PSF on the basis of a plurality of aperture values and the like so as to design a plurality of filters, and performs filter processing.
JP2008-245265A discloses an imaging device capable of easily detecting a resolution peak position, performing blurring processing for achieving favorable restoration, simplifying an optical system, reducing costs, suppressing the noise effect, and the like in a depth extension optical system. In the imaging device, filter processing corresponding to aperture stop information is performed.
In contrast, as an aperture of an aperture stop of the optical system becomes smaller, blurring in the photographed image, that is, small-aperture blurring gradually becomes more noticeable due to the light diffraction phenomenon. From the viewpoint of providing a high quality image, it is preferable to eliminate an effect of the small-aperture blurring that lowers the image resolution as much as possible, and there have been proposed various techniques of improving image quality by suppressing the effect of the small-aperture blurring.
For example, JP2007-292828A discloses a light amount adjustment device that avoids small aperture diffraction of an aperture stop. In the light amount adjustment device, two filter members, which have gradation ND regions where a transmittance continuously changes, are arranged such that the members face each other and shading change directions thereof are opposite, and are configured to be symmetrically movable.
JP2009-282551A discloses an imaging device in which light amount adjustment means provided in a photography lens device adjusts a light amount to a range where small aperture diffraction does not occur. The imaging device receives MTF characteristic data from the mounted photography lens device, and has control means for setting a utilization F number limit at which the small aperture diffraction occurs.